This invention relates to color photothermographic elements containing blocked developing agents and to methods of developing such elements.
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a Research Disclosure(129(1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity. In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving xcex2-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having xe2x80x9cxcex2-ketoesterxe2x80x9d type blocking groups (strictly, xcex2-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the xcex2-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The xcex2-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
There remains a need for blocked developers, useful in photothermographic elements, exhibiting good discrimination and low fog, which at the same time, exhibit good unblocking kinetics. Good discrimination and low fog are especially challenging when heating an element containing silver halide and blocked developers. It is an object to obtain a phototothermographic element or film incorporating blocked developing agents that provide good dye-forming activity and which, at the same time, yield good discrimination and little or no increased fog during development. There is especially a need for blocked developers which are useful in dry color photothermographic systems which do no require the application of processing solutions. These are usually developed at higher temperatures than systems in which some, albeit limited amounts of, aqueous solutions are employed during development, usually in the presence of a base.
With respect to developing agents for photothermogrpaphic color elements, there is a continuing need for photothermographic imaging elements that contain a developing agent in a form that is stable until development yet can be rapidly and easily developed once processing has been initiated by heating the element and/or by applying a processing solution, such as a solution of a base or acid or pure water, to the element. A completely dry or apparently dry process is most desirable. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
This invention relates to a color photothermographic element comprising a blocked developer that decomposes (i.e., unblocks) on thermal activation to release a developing agent. By thermal activation is meant heating at a temperature of at least 60xc2x0 C., preferably at least 80xc2x0 C., more preferably at least 100xc2x0 C., for 0.5 to 60 sec, preferably 1 to 60 sec, more preferably 2 to 30 sec. In dry processing embodiments, thermal activation preferably occurs at temperatures between about 80 to 180xc2x0 C., preferably 100 to 160xc2x0 C. In not completely dry development systems, thermal activation preferably occurs at temperatures between about 60 and 140xc2x0 C. in the presence of added acid, base and/or water. In one preferred embodiment of the invention, the photothermographic element comprises an effective amount of a thermal solvent. In another preferred embodiment of the invention, the photothermographic element comprises a mixture of organic silver salts (inclusive of complexes) at least one of which is a silver donor.
The invention additionally relates to a method of image formation having the steps of: thermally developing an imagewise exposed photographic element having a blocked developer that decomposes on thermal activation to release a developing agent to form a developed image. In one embodiment of the invention, a positive image can be formed by scanning the developed image to form a first electronic image representation (or xe2x80x9celectronic recordxe2x80x9d) from said developed image, digitizing said first electronic record to form a digital image, modifying said digital image to form a second electronic image representation, and storing, transmitting, printing or displaying said second electronic image representation.
The invention further relates to a one-time use camera having a light sensitive photographic element comprising a support and a blocked developer that decomposes to release a photographically useful group on thermal activation. The invention further relates to a method of image formation having the steps of imagewise exposing such a light sensitive photographic element in a one-time-use camera having a heater and thermally processing the exposed element in the camera.
In particular, the present invention is directed to photothermographic elements comprising blocked developers having a half-life (txc2xd)xe2x89xa620 min (as determined below). In has further been found that the specified half-life can be obtained by the use of activating groups in certain positions in the blocking moiety of the blocked developer, as explained more fully below with respect to the specified structures. By the term activating groups is herein meant electron withdrawing groups, heteroaromatic groups, or aryl groups substituted with one or more electron withdrawing groups.
More specifically, the color photothermographic element of the present invention comprises a blocked developer having a half life of less than or equal to 20 minutes and a peak discrimination, at a temperature of at least 60xc2x0 C., of at least 2.0, which blocked developer is represented by the following Structure I: 
wherein:
DEV is a developing agent;
LINK is a linking group;
TIME is a timing group;
n is 0, 1, or 2;
t is 0, 1, or 2, and when t is not 2, the necessary number of hydrogens (2-t) are present in the structure;
C* is tetrahedral (sp3 hybridized) carbon;
p is 0 or 9;
q is 0 or 1;
w is 0 or 1;
p+q=1 and when p is 1, q and w are both 0; when q is 1, then w is 1;
R12 is hydrogen, or a substituted or unsubstituted alkyl, cycloalkyl, aryl or heterocyclic group or R12 can combine with W to form a ring;
T is independently selected from a substituted or unsubstituted (referring to the following T groups) alkyl group, cycloalkyl group, aryl, or heterocyclic group, an inorganic monovalent electron withdrawing group, or an inorganic divalent electron withdrawing group capped with at least one C1 to C10 organic group (either an R13 or an R13 and R14 group), preferably capped with a substituted or unsubstituted alkyl or aryl group; or T is joined with W or R12 to form a ring; or two T groups can combine to form a ring;
T is an activating group when T is an (organic or inorganic) electron withdrawing group, an aryl group substituted with one to seven electron withdrawing groups, or a substituted or unsubstituted heteroaromatic group. Preferably, T is an inorganic group such as halogen, xe2x80x94NO2 or xe2x80x94CN; a halogenated alkyl group, for example xe2x80x94CF3, or an inorganic electron withdrawing group capped by R13 or by R13 and R14, for example, xe2x80x94SO2R13, xe2x80x94OSO2R13, xe2x80x94NR14(SO2R13), xe2x80x94CO2R13, xe2x80x94COR13, xe2x80x94NR14(COR13), etc. A particularly preferred T group is an aryl group substituted with one to seven electron withdrawing groups.
D is a first activating group selected from substituted or unsubstituted (referring to the following D groups) heteroaromatic group or aryl group or monovalent electron withdrawing group, wherein the heteroaromatic can optionally form a ring with T or R12;
X is a second activating group and is a divalent electron withdrawing group. The X groups comprise an oxidized carbon, sulfur, or phosphorous atom that is connected to at least one W group. Preferably, the X group does not contain any tetrahedral carbon atoms except for any side groups attached to a nitrogen, oxygen, sulfur or phosphorous atom. The X groups include, for example, xe2x80x94COxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94SO2Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94SO2N(R15)xe2x80x94, xe2x80x94CON(R15)xe2x80x94, xe2x80x94OPO(OR15)xe2x80x94, xe2x80x94PO(OR15)N(R16)xe2x80x94, and the like, in which the atoms in the backbone of the X group (in a direct line between the C* and W) are not attached to any hydrogen atoms.
W is Wxe2x80x2 or a group represented by the following Structure IA: 
Wxe2x80x2 is independently selected from a substituted or unsubstituted (referring to the following Wxe2x80x2 groups) alkyl (preferably containing 1 to 6 carbon atoms), cycloalkyl (including bicycloalkyls, but preferably containing 4 to 6 carbon atoms), aryl (such as phenyl or naphthyl) or heterocyclic group; and wherein Wxe2x80x2 in combination with T or R12 can form a ring (in the case of Structure IA, Wxe2x80x2 comprises a least one substituent, namely the moiety to the right of the Wxe2x80x2 group in Structure IA, which substituent is by definition activating, comprising either X or D);
W is an activating group when W has structure IA or when Wxe2x80x2 is an alkyl or cycloalkyl group substituted with one or more electron withdrawing groups; an aryl group substituted with one to seven electron withdrawing groups, a substituted or unsubstituted heteroaromatic group; or a non-aromatic heterocyclic when substituted with one or more electron withdrawing groups. More preferably, when W is substituted with an electron withdrawing group, the substituent is an inorganic group such as halogen, xe2x80x94NO2, xe2x80x94CN, or a halogenated alkyl group, e.g., xe2x80x94CF3, or an inorganic group capped by R13 (or by R13 and R14), for example xe2x80x94SO2R13, xe2x80x94OSO2R13, xe2x80x94NR13(SO2R14), xe2x80x94CO2R13, xe2x80x94COR13, xe2x80x94NR13(COR14), etc.
R13, R14, R15, and R16 can independently be selected from substituted or unsubstituted alkyl, aryl, or heterocyclic group, preferably having 1 to 6 carbon atoms, more preferably a phenyl or C1 to C6 alkyl group.
Any two members (which are not directly linked) of the following set: R12, T, and either D or W, may be joined to form a ring, provided that creation of the ring will not interfere with the functioning of the blocking group.
As indicated above, the specified half-life can be obtained by the use of activating groups in certain positions in the blocking moiety of the blocked developer of Structure I. More specifically, it has been found that the specified half-life can be obtained by the use of activating groups in the D or X position, with further activation to achieve the specified half-life by the use of activating groups in the one or more of the T and/or W positions in Structure I. As indicated above, the activating groups is herein meant electron withdrawing groups, heteroaromatic groups, or aryl groups substituted with one or more electron withdrawing groups. In one embodiment of the invention, the specified half life is obtained by the presence of activating groups, not only at the D or X position, but also at the T and/or W position in Structure I.
By the term inorganic is herein meant a group not containing carbon excepting carbonates, cyanides, and cyanates. The term heterocyclic herein includes aromatic and non-aromatic rings containing at least one (preferably 1 to 3) heteroatoms in the ring. If the named groups for a symbol such as T in Structure I apparently overlap, the narrower named group is excluded from the broader named group solely to avoid any such apparent overlap. Thus, for example, heteroaromatic groups in the definition of T may be electron withdrawing in nature, but are not included under monovalent or divalent electron withdrawing groups as they are defined herein.
In has further been found that the necessary half-life can be obtained by the use of activating groups in the D or X position, with further activation as necessary to achieve the necessary half-life by the use of electron withdrawing or heteroaromatic groups in the T and/or W positions in Structure I. By the term activating groups is meant electron withdrawing groups, heteroaromatic groups, or aryl groups substituted with one or more electron withdrawing groups. Preferably, activating groups are present, in addition to D or X, in at least one of T or W.
In a preferred embodiment of the invention, LINK is of structure II: 
wherein
Xxe2x80x2 represents carbon or sulfur;
Yxe2x80x2 represents oxygen, sulfur or Nxe2x80x94R1, where R1 is substituted or unsubstituted alkyl or substituted or unsubstituted aryl;
p is 1 or 2;
Z represents carbon, oxygen or sulfur;
r is 0 or 1;
with the proviso that when Xxe2x80x2 is carbon, both p and r are 1, when Xxe2x80x2 is sulfur, Yxe2x80x2 is oxygen, p is 2 and r is 0;
# denotes the bond to DEV;
$ denotes the bond to TIME or T(t) substituted carbon.